One objective of the proposed research is to improve understanding of the mechanism of DNA synthesis in animal cells, through application of broken cell systems for dissociation and reconstitution of the replication mechanism, and by purification and characterization of component parts. The second objective is to confirm the presence of oncornavirus-like particles in cytoplasm of human leukemic cells, and develop a more sensitive assay for the particles. If confirmed, additional studies will test the specificity of the association with malignant disease and with malignant cell behavior.